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ECG tutorial: Atrioventricular block

Jordan M Prutkin, MD, MHS, FHRS
Section Editor
Ary L Goldberger, MD
Deputy Editor
Gordon M Saperia, MD, FACC


Atrioventricular (AV) block may manifest as conduction delay in the AV node, intermittent failure of conduction from the atria to the ventricles, or complete AV block.


The PR interval (a measure of conduction between the atria and ventricles) includes the P wave (intra-atrial conduction) and the PR segment (conduction within the atrioventricular [AV] node and His-Purkinje system). First degree AV block, defined as a prolonged PR interval (>0.20 seconds), is not a true block but is rather delayed or slowed AV conduction. The conduction delay is most frequently in the AV node but may also be in the His-Purkinje system (waveform 1). A partial list of causes of first degree AV block include the following:

Underlying structural abnormalities of the node

An increase in vagal tone that causes a reduction in the rate of impulse conduction

Drugs that impair or slow nodal conduction including digoxin, beta blockers, and non-dihydropyridine calcium channel blocking agents

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Literature review current through: Nov 2017. | This topic last updated: Apr 05, 2016.
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